1. Technical Field
The present invention relates in general to computer network communications, and in particular, to the shaping and scaling of internetworking traffic in high speed network devices.
2. Background Art
With the increasing popularity of the Internet, traffic in some networks which link to popular Internet web sites may become congested periodically. If the network which carries this traffic has fixed bandwidth, significant traffic congestion can occur at peak traffic hours resulting in unacceptable delays. In order to accommodate a dynamic network like the Internet, internetworking infrastructures need a flexible traffic bandwidth scaler so that the network can scale its bandwidth based on the dynamic demand of the traffic.
In addition, many companies are now employing Internet technologies to build private intranets, enabling users in an organization to go beyond electronic mail and access critical data through web browsers. While intranet traffic is currently composed primarily of text, graphics and images, this traffic is expected to expand in the near term to include more bandwidth-intensive audio, video, voice and multimedia applications.
Network backup of servers and storage systems are common in many industries which require enterprise information to be archived. Backups occur during off hours and frequently require large amounts of bandwidth during a fixed period of time. The backup can involve gigabytes of data distributed over hundreds of servers and storage systems in a large enterprise.
As applications proliferate and demand ever greater shares of bandwidth at the desktop and as the total number of users continues to grow, the pressure for increased bandwidth will continue to grow at the desktop, the server, the hub and the switch. Organizations will need to migrate critical portions of their networks to higher-bandwidth technologies, such as Asynchronous Transfer Mode (ATM) and Gigabit Ethernet.
While Gigabit Ethernet technology is starting to evolve, ATM technology has been available for several years and the problem of traffic management in ATM networks has been under discussion for some time. However, the present invention is not limited to ATM or to Gigabit Ethernet technology and the basic concepts pertaining to traffic shaping apply to any high speed network.
Traffic supported by the network is classified according to several characteristics including bandwidth and latency. Bandwidth is the amount of network capacity required to support a connection. Latency is the delay associated with a connection. Traffic shaping is performed at the user-network interface. Devices that implement traffic shaping are typically network adapters in workstations, hubs, bridges, and routers.
Congestion can occur in any network whether it uses shared media like most LAN technologies, or wideband technologies such as ATM or Gagabit Ethernet. Congestion occurs whenever an application sends more data than the network can transmit with the available bandwidth. As more applications send data over the same network, the bandwidth available to any one application dynamically changes over time. When applications send more data than the network can handle, the network buffers fill up and can overflow. The application then has to retransmit data further adding to traffic congestion.
A variety of techniques have been applied to deal with the problem of network congestion control: these techniques include end-to-end, link-by-link, rate-based and credit-based traffic flow control. With end-to-end control, the network measures the minimum available bandwidth along an entire connection path and communicates the bandwidth to the application which then transmits at the appropriate rate. Each link along the path forwards the data as fast as it is received. With link-by-link control, each link along the connection path controls its traffic flow independently. Each link buffers data as needed to adjust the incoming speed to the outgoing speed.
More germane to the instant application are rate-based and credit-based techniques. In the rate-based technique, the network tells the application what transmission rate the sending device should use. When the network becomes congested, it reduces the rate and notifies the application. When the network is no longer congested, the rate is increased. In the credit-based technique, the network indicates to the sending device the amount of traffic space available in the network (credits). The network periodically replenishes the application's credits. When the network becomes congested, the application gets fewer credits and they are replenished less often. This causes the application to reduce its sending of data. When the network is no longer congested, the number of credits is increased and replenished more often.
In high speed networking, there has been much debate over whether a rate-based or a credit-based congestion control scheme is the more appropriate.
Therefore, there is a need for a high speed real-time bandwidth scheduler and shaper that combines the benefits of rate-based and credit-based techniques.